Walking beam furnace for effecting different feed speeds of the charge



March 19, 1968 A. BORGKVIST 3,373,980 WALKING BEAM FURNACE FOR EFFECTING DIFFERENT FEED SPEEDS OF THE CHARGE Filed June 2, 1966 3 Sheets-Sheet 1 FIG.1

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WALKING BEAM FURNACE FOR EFFEGTING DIFFERENT FEED SPEEDS OF THE CHARGE Filed June 2, 1966 5 Sheets-Sheet 2 w R.! mu N mw B e h S n "A E 0a R BY W JWEWPMJQ Afto rhegs T A. BORGKVIST 3,373,980 FURNACE FOR EFFECTING DIFFERENT SPEEDS OF THE CHARGE March 19, 1968 WALKING BE 3 Sheets-Sheet 5 Filed June 2, 1966 w a .N @E

INVENTOR.

United States Patent Office 3,373,980 Patented Mar. 19, 1968 3,373,980 WALKING BEAM FURNACE FOR EFFECTING DIFFERENT FEED SPEEDS OF THE CHARGE Tage Anshelm Borgkvist, Stockholm, Sweden, assignor to Aktiebolaget Tabougnar, Stockholm, Sweden, a Swedish joint-stock company Filed June 2, 1966, Ser. No. 554,736 Claims priority, application Sweden, Feb. 28, 1966, 2,57 3/ 66 6 Claims. (Cl. 263-6) ABSTRACT OF THE DISCLOSURE A walking beam furnace comprises a pre-heating zone and a final heating zone arranged to give charges different feed speeds through the zones over a stationary hearth. The walking beams extend in an undivided manner through all zones of the furnace and are arranged to be reciprocated at different levels in relation to the stationary hearth so as to effect the feed of the charge.

This invention relates to a method and construction of a walking beam furnace adapted to effect by means of the same feed machinery different feed speeds of the charge through different furnace zones.

For heating special steels, for example high-speed steel, tool steel etc. the material must be given a special temperature-time curve which corresponds with the sensitivity of the material to temperature and cracks and with the risk of decarburization.

This means, that the steel is heated relatively carefully and slowly to a special temperature, say 800 C., whereafter it is finally heated to forging temperature, say 1150- 1200 C., in the shortest possible time. The pre-heating to 800 C. is carried out in a special part of the furnace, the pre-heating zone which comprises a separate furnace chamber and an individually controlled burner equipment for maintaining a constant temperature, say 850 C. Through this part of the furnace the material must be advanced at a special speed, in order to provide the steel a uniform temperature both across the entire exposed surface and from the surface to the centre of the material.

In the final part of the furnace, the final heating zone, a higher temperature, say 12501300 C., is maintained by means of a similar separate furnace chamber with a burner and instrument equipment of its own. Due to the higher difference in temperature between the furnace atmosphere and the charge, the final temperature of the charge can be achieved in a shorter time than in the pre-heating zone. This is of importance for preventing the formation of too much scale and decarburization, and it implies a shorter final heating zone and/ or a more rapid feed.

The slower feed through the pe-heating zone, followed immediately by a feed at a very high speed through the final heating zone, is carried out in a walking beam furnace usually in such a manner, that the advanced beam or beams are divided in the longitudinal direction where the change of speed in the furnace is desired, whereafter every part is provided with its own lift and feed machinery, or the two parts are connected in such a manner, that they are lifted and lowered individually, but reciprocated together, for which purpose two individual lift machineries but only one feed machinery are required.

The divided walking beam involves the disadvantage that by the division additional slits, and thereby cooling portions are produced which deteriorate the thermal efficiency of the furnace. The walking beam construction, moreover, becomes substantially more complicated.

The present invention eliminates the said disadvantages in a simple and cheap manner.

The invention has as its object to effect the different feed speeds by means of an entire and undivided walking beam or by several undivided walking beams, by employing only one lifting and one feed machinery. This object is achieved by giving the sttaionary hearth different levels in the different heating zones and the walking beam different lifting positions.

An embodiment of the invention is described in the following, reference being had to the accompanying drawings whereon FIG. 1 shows a longitudinal section through the furnace along the line I-I in FIG. 2,

FIG. 2 shows part of a cross-section along the line IIII in FIG. 1 through the stationary hearth and walk. ing beams of the furnace,

FIGS. 3 and 4 show in a schematic manner different working steps,

FIG. 5 shows a modification of the arrangement according to FIG. 1.

The furnace shown comprises a pre-heating zone 1 and a final heating zone 2, between which zones there is a free passage for the charge. The stationary hearth comprises longitudinal beams 3 which in a usual manner extend through the two zones 1 and 2. Walking beams 4 arranged between the beams 3 are adapted to carry out reciprocating as well as lifting and lowering movements. Up to this point the furnace is in agreement with known types.

The novelty lies in the feature that the stationary hearth has different levels in the different heating zones. Thus, the stationary beams 3 have a difference in level at the boundary 5 between the pre-heating zone 1 and the final heating zone 2. The charge 6, thus, assumes different levels, according to the zone in which it is situated. The feed into the furnace is carried out from the furnace end 7 and towards the opposite end 8. The walking beams 4 reciprocate on the rolls 9. The drive means are not shown, because the said beams can be operated in a conventional manner, for example by a hydraulic engine.

The rolls 9 are arranged to be lifted and lowered variably, in that arms 10 on which the rolls are mounted are swung upwards and downwards via the rotation of shafts 11 on which the arms 10 are secured. The rotation of the shafts 11 can be effected, for example, by a hydraulic, pneumatic or electric motor. By swinging the arms 10, thus, the walking beams 4 can be brought into a bottom position B and a top position D as well as into optional positions therebetween. In the bottom position, the walking beam carries out its return movement.

FIG. 2 shows a cross-section through a portion of the stationary hearth and the walking beams 4-. The stationary hearth, thus, comprises beams 3 provided with cams 12 for supporting the charge 6. The walking beams 4 are located between the beams 3, and in the position B there is no contact with the charge 6', whilst in position D the charge is lifted from the beam 3 and can be moved with the movement of the walking beam.

FIG. 3 shows in a schematic manner a working step of the arrangement. The walking beams are in the top position D and lift the charge 6 from the stationary hearth 3 both in the pre-heating zone 1 and in the final heating zone 2. The different levels of the stationary hearth in the zones are marked by dashed lines, the designation 31 being for the pre-heating zone and the designation 32 for the final heating zone. In FIG. 3, thus, the walking beams 4 lift the charge in both of the zones and are then pushed ahead on the rolls 9 whereby the charge is taken along. The walking beams 4 are then lowered into bottom position B and the charge assumes a new position on the stationary hearth 3. In the bottom position, the walking beams return to the starting position.

FIG. 4 shows another working step. The walking beams are brought onto a level C located between the levels 31 and 32 of the hearth. On this level the charge is lifted only in the final heating zone 2 and advanced with the movement of the walking beams to the right. As regards the reciprocating movement of the walking beams, this can be effected by a drive machinery of variable speed, so that the feed in connection with the lifting of the charge in one zone can be made more rapid than in another zone. The present invention renders it possible to empty the final heating zone entirely of material without disturbing the charge in the pre-heating zone, and to return the material in the final heating zone back to the pre-heating zone, in the event of a breakdown in the rolling mill or forging press.

A particularly interesting modification of the invention is shown schematically in FIG. 5, from which it is understood that the same effect in walking beam feed as described above can be obtained when the hearth 3 is plane without steps, and instead the walking beams are formed with levels of different height at 5', the higher level 41 corresponding to the lowered portion 32 of the hearth according to FIG. 1, and the lower level 42 of the walking beam corresponding in the same manner to the higher portion 31. In their remaining parts, the constructions according to FIG. 5 and FIG. 1 are identical.

The invention is not restricted to only one step 5, but a walking beam furnace can be provided with any number of control zones and also with any number of level differences. Nor is the level difference restricted to a certain value, but it may vary according to the billet and material dimensions.

What I claim is:

1. A walking beam furnace comprising pre-heating and final heating Zones and adapted to give charges different feed speeds through the zones over a stationary hearth. the feed movement of the charge being effected by the walking beams, said walking beam or beams extending undivided through all zones of the furnace and being arranged to be reciprocated on different levels, which levels the walking beams are caused to assume by means of a lifting and lowering arrangement, the said stationary hearth and the walking beams being formed in the different zones for the charge with separate levels in relation to each other.

2. The walking beam furnace according to claim 1, wherein the stationary hearth is stepped, the boundary between the different heating zones being located at the transition from one step to an adjacent step.

3. The walking beam furnace according to claim 1, wherein the lifting and lowering arrangement is variable.

4. The walking beam furnace according to claim 1, wherein the reciprocating speed of the walking beams is variable.

5. The walking beam furnace according to claim 1, wherein the walking beams are stepped.

6. A method for feeding in a walking beam furnace with separate heating zones as defined in claim 1, according to which method the charge in resting position is brought onto different levels in the separate zones, the walking beams lifting only charge in a desired zone or zones and being moved in this lifted position in the direction of feed and thereafter being lowered again.

References Cited UNITED STATES PATENTS 1,133,789 3/1915 Becht 198219 XR 2,188,309 1/1940 Pentecost 198-2l9 XR 2,722,406 11/1955 Kurek 198219 XR CHARLES J. MYHRE, Primary Examiner.

FREDERICK L. MATTESON, JR., Examiner.

A. D. HERRMANN, Assistant Examiner. 

